Algal diversity of temperate biological soil crusts depends on land use intensity and affects phosphorus biogeochemical cycling

Biological soil crusts (BSCs) form the most productive microbial biomass in many drylands and disturbed areas with a diverse 10 microalgal community as key component. In temperate regions, BSCs are also common, but generally less studied, and they conduct important ecological functions, like stabilization of soil and enrichment of nutrients. Changes in land use and its intensity strongly influence biodiversity per se and it’s role for ecosystem processes, particularly in regions which are densely populated like Europe. But systematic studies on land use (i.e. management intensity) gradients in temperate forests on BSCs are missing up to now. To close this gap of knowledge and enhance the understanding of management effects on BSCs, 15 Cyanobacteria and eukaryotic microalgae as key primary producers of these communities were identified from pine and beech forests under different management regimes. Algae were identified morphologically based on enrichment cultivation and categorized in either coccal taxa, which occur typically in high diversity, or filamentous taxa, which have the potential to initiate BSC formation. In total, 52 algal species were recorded, most from the phylum Chlorophyta, followed by Streptophyta and Heterokontophyta; Cyanobacteria were much less abundant in temperate forest BSCs. The most abundant crust-initiating 20 filamentous algae were three species of Klebsormidium (Streptophyta) a ubiquitous genus often associated with BSCs worldwide and a high tolerance to low pH. Increasing management intensity resulted in a higher richness of algae, especially the proportion of coccal algae rose. Furthermore, the proportion of inorganic phosphorus was positively correlated with the algal richness, indicating that higher diversity of algae results in a more closed P cycle. Thus, management of forests has an impact on the diversity of phototrophic organisms in BSCs, which in turn affects P cycling in the BSC. 25 key words: biological soil crusts, forest, management intensity, phosphorus, algae richness, Klebsormidium Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-365 Manuscript under review for journal Biogeosciences Discussion started: 27 September 2017 c © Author(s) 2017. CC BY 4.0 License.

Our results based solely on the identification of cultivable algae.We also observed the algae directly in the crust.But in this case it is impossible to identify the algae correctly for the following reasons: although the crust were rewetted and incubated for a short time, not all algal species are in a reasonable morphological state because of spore formation, presence of extracellular matrix (mucilage etc.), cellular features (accumulation of storage compounds etc.) etc, all of which hamper unambiguous identification based on morphological characteristics.Normally in direct observations, only few cells of one species can be well observed; for correct morphological identification many cells of the same species in different states are necessary.For example, for identification of Chlorococcum-species it is necessary to observe also young cells.In a mixed community like in the soil crusts, it is hard to tell if one algae represents a young status of Chlorococcum, or if it belongs to some Chlamydomonas-like morphotype.This is only possible in a well prepared enrichment culture, where colonies of algae are separated on the agar.Also most of the detailed morphological descriptions in "Syllabus der Boden-, Luft-und Flechtenalgen" are based on algal cultures.It is known that environmental factors influence the morphology.Therefore, correct identification is only possible with the same or very similar approaches like in algal handbooks; in this case, to use common alga media.
The Referee is right, with direct observation we could have also said something about the abundance and thus about biodiversity.As we can only rely on presence/absence data, we changed the wording throughout the text and rather use "richness" instead of "diversity" to avoid misleading implications.As the same misunderstanding applies for "community composition", thus, we also changed the wording to presence or absence of individual algal (for example, p. 4, ls. 24).As a second parameter, we showed similarity between single plots by presence / absence of individual species, which combines the total number and the identity of the algal species.)I would appreciate if the Introduction provided more information on the BSCs in forests.Most part of the Introduction introduces BSCs as we know them from the arid regions, including their ecological roles and what threatens them there.But the desert areas and open arid sites in temperate regions are very different from temperate forests, so I think it would be useful if the authors talked a little bit more about whether these facts are true for forests as well.How are the BSCs in forests defined and established?Is "green cover" really equal to BSC? (If "just" green cover was present on a statue or a wall, it would be probably called biofilm, rather than a crust.)Why should they be interesting?Maybe providing more information about the specific sampling sites would help to clarify it as well (did the authors have to remove the litter first to look for the green cover or was the sampling done in open sites in forest, : : :).I know the sampling itself was done as part of different study, but I think this information is worth repeating (maybe as part of Table 1), because it would be important also when looking at the algal diversity and which exact factors influence it.We understand the doubts of the Referee, because most literature deals indeed with BSCs from arid regions.Thus, we followed the suggestion to enhance the introduction part.We included some pictures from our sampling campaign, which might help to get an impression of BSCs from temperate forest (figure 1).p. 2, ls.7 Although BSCs received raising interest in the past years, for example, as global player in terrestrial nitrogen fixation (Elbert et al. 2012), reports on BSCs from forests are very rare (Seitz et al. 2017).Under mesic conditions BSCs have to compete with vascular plants and thus their development is often limited.Especially in forests the limitation of light and the occurrence of litter restricts the crust development.But disturbances of the higher vegetation layer change this competitive situation and allow the development of BSCs.Such disturbances occur frequently in temperate forests, for example, natural tree fall, pits of wild boars, litter free spots at slopes, molehill-like humps, or human-induced disturbances such as skid trails and clear-cut areas.Especially tree falls after storm events is a rising problem in Europe due to increasing number and strengths of storms, probably because as a consequence of global change (www.dwd.de).At such spots, BSCs typically serve as pioneer vegetation for colonialization of naked soils after heavy disturbance and destruction of intact forest ecosystems.Thus, BSCs can protect disturbed areas, for example, from erosion and due to the biological introduction of carbon and nutrients into the soil regrowth of vascular plants is initiated (Seitz et al., 2017).Seed germination of vascular plants strongly benefits from biogeochemical activities of BSCs (Li et al., 2005;Su et al., 2009).
p. 3, ls.29 Samples were taken from natural, protected forests and from managed forest (age-class forest) on disturbed areas where BSCs could develop on litter free bare soil (for illustration see Figure 1).p. 10, ls. 8 BSCs are able to coexist in temperate forest ecosystems, because natural and human-induced disturbances, such as wind fall and skid trails, regularly provide free space for crusts to develop.
I am a little confused about the terms silvicultural management intensity, managed forest, and so on.Could the authors please specify more what it means in practice with regard to the BSCs?Do I understand it right that in more managed forests the soil is more often disturbed by heavy machines, traffic, etc? Maybe the authors could provide more detail on how the protected forest differed from the managed forest specifically with regard to the crusts (overall soil cover, amount of dead biomass on the ground, density of the tree stand,: : :).Also it is not clear which samples were collected from the protected and which from the managed forest.The only indication the readers get is that the SMI is lower for natural forests and higher for pines.But the authors do not specify anywhere above/below what number the SMI needs to be so the forest can be considered protected/managed.Thus, in Table 1 it is not possible to find out which and how many samples were taken from which protected vs. managed type of forest (and I was not able to find it anywhere else in the text as well).
We understand that with more details on the silvicultural management intensity and a careful wording we can avoid confusion about it.We added the requested information if the sampling sites were located in a natural or managed forest in table 1 as well as in the text.p. 4, ls. 29 In natural forests, no management was conducted, meaning that fallen trees were left in place and no trees were cut.
In managed age-class forests, the stands were disturbed due to e.g.usage of skid trails and removal of dead trees as well as tree cut.[…] The natural forest has a lower SMI than the managed forest; a pine stand has a higher SMI than a beech stand; high stand density is reflected by a high SMI. p. 8,ls. 28 The richness of algal species as well as the proportion of coccal algae were positively correlated with the silvicultural management index (SMI), which means that we discovered more alga species in BSCs from managed than from natural forest ecosystems.
Even though the title promises information about the phosphorus biogeochemical cycling, the readers do not learn much new information and the data connected with P do not seem to be significant.The previous paper of the authors (Baumann et al., 2017) often referenced in the text seem to provide much detail information.
We understand the arguments of the Referee, which is in accordance with the second Referee.Of course, we don't want to make false promises.Thus, we changed the title to "Algal richness of temperate biological soil crusts depends on management intensity and correlates with inorganic phosphorus".

Specific Comments and Technical Corrections:
I would not mix algae and cyanobacteria under the name algae.Instead of ": : :52 different algae species: : :" I would consider "51 algae and a cyanobacterium" to be more precise as the prokaryotic and eukaryotic organisms are not included together.Good point which we addressed.The goal of the presented study was to describe and characterize a biological soil crust that occurs in a temperate forest in Germany (p3.L 3).This was done by assessing the species composition and evaluating the effects of the crust on the soil chemistry (C;N;P).In a second step effects of land use on the number of algal species of this crust was examined.The study is well written and might represent a new and interesting contribution.Nevertheless, there are some major drawbacks, which should be considered before publication.

1.) Definition of BSC in forests
This is a critical topic in this manuscript because the authors do not provide enough explanations here.In the classic BSC literature, a BSC is found in " regions where water availability limits vascular plant cover" (Belnap, Weber, Büdel 2016) or "in arid and semiarid lands throughout the world, where the cover of vegetation is sparse or absent" (Belnap and Lange 2003).Both definitions are taken from the exactly cited works as given in the introduction.In the present study, the authors examine a crust from a temperate forest which contradicts this definition.A temperate forest is a habitat with a dense vegetation cover and a biome characterized by a mean precipitation between 750 and 1500 mm.This sets the presented study into a critical position for two reasons.First, because the authors do not indicate this strong discrepancy between the classical BSC definition and their own approach and explain why they still aim to refer to a BSC in this context.Secondly, because there is a vast number of publications handling effects of land use on forest understory vegetation as well as microflora and -fauna that is not considered in the discussion.It is a recent trend in BSC literature that more and more BSC are found and described in humid and forest ecosystems and I would, therefore, like to encourage to authors to critically discuss this point here, especially because this publication is part of a special issue about BSC.This study provides a chance to introduce BSC in this ecosystem if the authors try to catch up on this point and explain carefully.Statements, like given in P2l7 or P2l17 about the lack of information regarding temperate forest BSC, might just be a result from a limited literature search that focused only on BSC and not on studies regarding understory community assemblies in temperate forests.Nevertheless, as it stands now I cannot see the difference between the studies on understory forest vegetation and the presented study.In this context, the study would clearly benefit from pictures showing this crust type and how it is assembled.
We enlarged the introduction section for a clearer explanation of biological soil crusts in temperate forests and the differences to crusts from arid regions, where BSCs are the dominating life form.We included some pictures from our sampling campaign, which might help to get an impression of BSCs from temperate forest (figure 1).p. 2, ls.7 Although BSCs received raising interest in the past years, for example, as global player in terrestrial nitrogen fixation (Elbert et al. 2012), reports on BSCs from forests are very rare (Seitz et al. 2017).Under mesic conditions BSCs have to compete with vascular plants and thus their development is often limited.Especially in forests the limitation of light and the occurrence of litter restricts the crust development.But disturbances of the higher vegetation layer change this competitive situation and allow the development of BSCs.Such disturbances occur frequently in temperate forests, for example, natural tree fall, pits of wild boars, litter free spots at slopes, molehill-like humps, or human-induced disturbances such as skid trails and clear-cut areas.Especially tree falls after storm events is a rising problem in Europe due to increasing number and strengths of storms, probably because as a consequence of global change (www.dwd.de).At such spots, BSCs typically serve as pioneer vegetation for colonialization of naked soils after heavy disturbance and destruction of intact forest ecosystems.Thus, BSCs can protect disturbed areas, for example, from erosion and due to the biological introduction of carbon and nutrients into the soil regrowth of vascular plants is initiated (Seitz et al., 2017).Seed germination of vascular plants strongly benefits from biogeochemical activities of BSCs (Li et al., 2005;Su et al., 2009). p. 3, ls. 29 Samples were taken from natural, protected forests and from managed forest (age-class forest) on disturbed areas where BSCs could develop on litter free bare soil (for illustration see Figure 1).p. 10, ls. 8 BSCs are able to coexist in temperate forest ecosystems, because natural and human-induced disturbances, such as wind fall and skid trails, regularly provide free space for crusts to develop.

2.) Diversity
According to the title, algal diversity was evaluated in this study but I wonder why this terminology was used here.Species diversity consists of three components: species richness, taxonomic or phylogenetic diversity and species evenness.With these parameters, diversity or diversity indices can be calculated.In the given study the authors provide species richness and frequency data and I think it would be more precise to refer to these (or species composition) throughout the text, rather than to diversity or even biodiversity, which wasn0t studied here.The terminology should be consistent throughout the text.(examples of the used terminology in the manuscript: diversity, biodiversity, alga richness, algal richness, community composition of alga, richness of alga, algal species richness, algal biodiversity, biodiversity of microalgae and cyanobacteria) The Referee is right, we estimated only the richness of cultivable algae.The drawbacks of our method is described well in the MS (p. 6. ls. 25).As we can only rely on presence/absence data, we changed the wording throughout the text and rather use "richness" instead of "diversity" to avoid misleading implications.As the same misunderstanding applies for "community composition", thus, we also changed the wording to presence or absence of individual algal (for example, p. 4, ls. 14).As a second parameter, we showed similarity between single plots by presence / absence of individual species, which combines the total number and the identity of the algal species.)

3.) Phosphrous biogeochemical cycling
The title promises information about phosphorus biogeochemical cycling and in the introduction, the authors state that "the effect of BSC algal biodiversity on C, N, and P content, in particular on the different fractions of P was assessed".Nonetheless, different P proportions are not shown but taken from a previous study from the authors, that is cited very often throughout the article.The only data given here are C, N, and P contents for n=19 samples which seems to be a little database for the conclusions drawn.I also wonder about the statistical test that was chosen to interpret the results, because correlation does not imply causation and the authors should be careful with interpreting their results in such a broad way.
We understand the arguments of the Referee, which is in accordance with the first Referee.Of course, we don't want to make false promises.Thus, we changed the title to "Algal richness of temperate biological soil crusts depends on management intensity and correlates with inorganic phosphorus".p. 10, ls.14 Increasing algal richness in BSCs was supposed to enhance biogeochemical cycling of nutrients, as documented for P compared to bare soils, but this hypothesis could not be proven.Nevertheless, the fraction of inorganic P showed tendencies towards a correlation with BSC algae, especially with filamentous species.Consequently, the present study gives the first hint of a potential relation between the biogeochemical cycles in BSCs and algal species.This relation should be studied in more detail, for example, by gene expression analyses to understand if and how algae in BSCs influence the cycling of P. Also, forthcoming studies should include other crust-associated organisms, like fungi and bacteria, to identify key players on the ecological role of BSCs in the P cycle.

4.) Land use intensity
Land use intensity was approximated by applying the silvicultural management index.This was determined for each study site.In table 3 it is given that SMI affects algal richness with 30,5% and the proportion of filamentous algae with 37.7%.It is stated in p 6 L 13 that higher SMI resulted in higher species richness given in Figure 2. Figure 2 represents a pie chart with mean phylum numbers of all plots.So I assume Figure 4 should show this.This graph is difficult to understand.The caption needs to be improved and explain what the symbols show.I assume these are the different forest stands and the correlation was pooled stand independently?(So why include this information?).What was the correlation index?Where is the information about coccal algae that is given in the text?What does "richness of algae" mean?From the discussion it becomes clear that SMI basically effects the BSC composition via tree density, thus shading and light availability.Therefore, it is critical to refer to land use in this context.The authors need to define how they expect SMI to affect the BSC directly or explain the SMI was used as a proxy for tree stand density.
We understand that with more details on the silvicultural management intensity and a careful wording we can avoid confusion about it.p. 4, ls.29 In natural forests, no management was conducted, meaning that fallen trees were left in place and no trees were cut.
In managed age-class forests, the stands were disturbed due to e.g.usage of skid trails and removal of dead trees as well as tree cut.[…] The natural forest has a lower SMI than the managed forest; a pine stand has a higher SMI than a beech stand; high stand density is reflected by a high SMI.
p. 8, ls.28 The richness of algal species as well as the proportion of coccal algae were positively correlated with the silvicultural management index (SMI), which means that we discovered more alga species in BSCs from managed than from natural forest ecosystems.former mining sites) (Fischer et al., 2010b;Langhans et al., 2009;Lukešová, 2001;Schulz et al., 2016).
P2l11: richness of BSC organisms?p. 2, l. 30 the number of microalgae species in BSCs P2l22: Elbert et al. 2012 does not distinguish between different crust components and instead pools information from all photoautotrophs in cryptogamic covers.Please find an adequate citation for your statement.p. 2, l. 31 (Belnap et al., 2001) P2l24: please provide a precise citation for this statement.changed to Büdel et al., 2016 -P3l6: this information is irrelevant heredeleted P3l13: which plots were these?-P3l16: what is a microecosystem?lastsentence was deleted P4l2-8: I wonder whether this cultivation technique does not influence the species assembly because some species might be excluded and others overestimated.p. 6, ls.29 Nevertheless, the given number is most probably an underestimation of the real algal richness because our results are based on enrichment cultivation followed by morphological assignment.Enrichment cultivation typically covers mainly cultivable algae, which represent only a small part of all phototrophic microorganisms in BSCs (Langhans et al., 2009).A recent paper comparing metagenomic data with morphological data based on enrichment cultivation estimated a match of about 10% of all microalgae in a polar BSC (Rippin et al., 2018).Furthermore, it is not always possible to distinguish dormant from currently active microalgae.However, direct observation of a BSC sample under the microscope gives at least a first hint for the dominant active organisms.Using this approach we could prove that all filamentous algae were abundant and always vital in the BSC samples.The morphological identification of algae has known challenges, for example, sibling species have similar characteristics but are genetically distant (Potter et al., 1997).To overcome these limitations, researchers proposed to combine molecular and morphological methods, since molecular techniques alone sometimes also fail to detect some taxa based on problems with DNA extraction, appropriate primers etc. (Büdel et al., 2009;Garcia-Pichel et al., 2001).
P4l16-18: how were the frequency data gained?How were the 'proportion' data generated?p. 4, ls. 25 Further, the identified algae were categorized in filamentous or coccal life form, because both differ in their ecological function.Filamentous algae, in contrast to coccal algae, have the potential to initiate crust-formation and stabilize soil particles by gluing them together.
P4l25: is richness here the total species number?-P5l3: alga richness?Did you exclude the Cyanobacteria?p. 4, ls.22 richness of algae (total number of algae and cyanobacteria species per sample) P4l7: specify community composition of algaep.4,ls.23 As a second parameter for biodiversity the similarity between single plots is shown as reflected in the presence / absence of individual species which combines the total number and the identity of all algal taxa observed.P10l4: This statement about the moss protonema is surprising because this was not studied here and just occurred as a side note in the discussion.Why is this included in the conclusion?as suggested, deleted from the conclusion P10l8: A citation of a different study in the conclusion seems misplaced.Consider summarising the data presented here.We rewrote this paragraph accordingly.

Introduction
Biological soil crusts (BSCs) occur as important and often dominant vegetation on all continents on Earth, predominantly in arid and semi-arid habitats, but also in temperate regions (e.g., Belnap et al., 2001;Weber et al., 2016).In semiarid and arid environments, BSCs were studied, for example, in deserts of Israel and USA or but also in polar regions (Borchhardt et al., 2017;Flechtner et al., 1998;Kidron et al., 2010).In temperate regions these habitats include dunes with sparse higher vegetation or disturbed areas in open sites (like e.g.former mining sites) (Fischer et al., 2010b;Langhans et al., 2009;Lukešová, 2001;Schulz et al., 2016).
Although BSCs received raising interest in the past years, for example, as global player in terrestrial nitrogen fixation (Elbert et al. 2012), reports on BSCs from forests are very rare (Seitz et al. 2017).Under mesic conditions the BSCs have to compete with vascular plants and thus their development is often limited.Especially in forests the limitation forof light and the occurrence of litter restricts the crust development.But disturbances of the higher vegetation layer change this competitive situation and allows the development of biological soil crustsBSCs.Such disturbances occur frequently in temperate forests, for examplexample,e natural tree fall, pits of wild boars, litter free spots at slopes, or molehill-like humps, or are humaninduced disturbances such aslike skid trails and clear-cut areas.Especially tree falls after storm events is a rising problem in Europe due to increasing number and strengths of storms, probably because as a consequence of global change (www.dwd.de).
At thesesuch spots, biological soil crustBSCs can develop andtypically serve as pioneer vegetation a starting point offor colonialization of naked soils after heavy disturbance and destruction of intact forest ecosystems.Thus, soil crustsBSCs can protect disturbed areas, for example, from e.g.erosion and due to the biological introduction of carbon and nutrients into the soil until the successful regrowth of vascular plants is initiated (Seitz et al., 2017) and even enhance the process of regrowth.
It has been shown that spermSeed germination of vascular plants strongly benefits from biological soil crustsbiogeochemical activities of BSCs (Li et al., 2005;Su et al., 2009).
Although BSCs received raising interest in the past years, reports on BSCs from temperate forests are still missing up to now.Disturbance of BSCs due to land use has been reported to have strong negative effects on BSCs cover, which resulted in higher soil erosion and C and N losses from in the top soil (Barger et al., 2006;Belnap, 2003).Studies on the effect of land use on BSCs were mainly conducted in arid and semiarid regions.These studies reported, for example, a strong negative influence of intensive livestock grazing on BSC cover due to trampling with a recovery period of up to 27 years (Concostrina-Zubiri et al., 2014;Gomez et al., 2004;Williams et al., 2008).Also, ploughing in Australian sand plains reduced the BSCs cover dramatically (Daryanto et al., 2013).In contrast, there are no reports on land use effects in temperate regions or aspects of land use other than grazing on BSCs, likesuch as, for example, fertilization of grass or arable land and silvicultural management.
BSCs can be characterized as "ecosystem-engineers" forming water-stable aggregates that have important ecological roles in primary production, nitrogen cycling, mineralization, water retention, and stabilization of soils (Castillo-Monroy et al., 2010;Evans and Johansen, 1999;Lewis, 2007).While the role of BSC in the C-and N-cycle is well documented, less is known about their role in P cycling.However, recent studies indicated that the numberamount of microalgale species in BSCs is related to soil P content (Baumann et al., 2017;Schulz et al., 2016).Also, soil texture and carbon content seem to affect the BSC community .But still, only little is known about environmental factors that shape BSC communities and how BSCs in turn affect soil characteristics.
Disturbance of BSCs due to land use has been reported to have strong negative effect on BSCs cover, which resulted in higher soil erosion and C and N loss in the top soil (Barger et al., 2006;Belnap, 2003).Studies on the effect of land use on BSCs were up to now exclusively conducted in arid regions.These studies reported, for example, a strong negative influence of intensive livestock grazing due to trampling on BSC cover with a recovery period of up to 27 years (Concostrina-Zubiri et al., 2014;Gomez et al., 2004;Williams et al., 2008).Also ploughing in Australian sand plains reduced the BSCs cover dramatically (Daryanto et al., 2013).In contrast, there are no reports on land use effects in temperate regions or aspects of land use other than grazing on BSCs, like, for example, fertilization of grassland or arable land and silvicultural management.
Cyanobacteria and microalgae represent the most important phototrophic components of BSCs along with macroscopic lichens and bryophytes (Belnap et al., 2001).Eukaryotic algae are probably the least studied phototrophs in BSCs, although these organisms are an essential component of BSCs such communities because of their major contribution to C fixation (Büdel et al., 2016).BSC algae can be categorized in as two functional groups.First,(I) filamentous algae as major BSC forming taxa that stabilize soil particles by gluing them together due to the presence/excretion of sticky mucilage.The filamentous forms occur usually in low diversity but produce high biomass.And second,(II) coccoid algae which are attached to the soil particles or other algae and typically occur in higher diversity but lower biomass (Büdel et al., 2016).
Filamentous cyanobacteria, especially of the genus Microcoleus, are often the dominant phototrophic organisms in most BSCs of drylands and in dunes from temperate regions (Garcia-Pichel et al., 2001;Schulz et al., 2016).They are described as important for BSC formation due to their ability to produce mucilage sheadths and extracellular polymeric substances forming a sticky network between soil particles (Gundlapally and Garcia-Pichel, 2006).In temperate regions, this key function is often taken over by filamentous eukaryotic algae, like Klebsormidium, Xanthonema or Zygogonium (Fischer and Subbotina, 2014;Lukešová, 2001;Pluis, 1994).
The aim of the present study was to characterize for the first time the algal community in BSCs collected in temperate forests of different silvicultural management intensities.In a previous study we presented hints that differences of algal richness in BSCs contributing to P cycling wereare detectableed, and that the data indicated that BSCs asre particularly involved in the transformation of inorganic P to organic P compounds, and thus playing a key role in the biologically driven P cycling in temperate soilsprovided a very detailed picture on the distribution of P content, P pools and P species in temperate BSCs and adhering soil (Baumann et al., 2017).Differences of algal richness in BSCs contributing to P cycling were detected, and the data indicated that BSCs are particularly involved in the transformation of inorganic P to organic P compounds and thus play a key role in the biologically driven P cycling in temperate soils.In addition, BSCs responded differently to management intensity depending on forest type (beech versus pine).While algal species richness of BSCs was considered as sum parameter, detailed information on the biodiversity species occurrences is still missing (Baumann et al., 2017).Therefore, in the present study we identified algal species in a temperate forests and investigated for the first time in detail the influence of silvicultural management intensity on algal biodiversity richness and species identification in BSCs collected at the same plots as in Baumann et al. (2017), plus some additional sampling sites.The correlation of BSC algal biodiversity richness and C, N and P content, in particular on the different fractions of P, was assessed in order to uncover (disentangle?) the relation between biogeochemical cycles in biological soil crustsBSCs and the BSC-associatedunderlying alga species.

Study site
BSC samples were collected in June 2014 and 2015 from plots of theas part of the DFG German priority program 1374 Biodiversity Exploratories (Fischer et al., 2010a).Forest plots were sampled in the Schorfheide-Chorin Biosphere Reserve in Northeast Germany.The plots differed in the dominant tree species: Scots pine (Pinus sylvestris L.) or European beech (Fagus sylvatica L.).Samples were taken from natural, protected forests and from managed forest (age-class forest) on disturbed areas where BSCs could develop on litter free bare soil (for illustration see fFigure 1).
The top millimeters of soil, on which BSC had been visually detected as green cover, were collected by pressing a petri dish in the respective crust and removing gently with a spatula.After transportation to the lab the upper two millimeters of the crust was were separated from the adhering soil underneath using a razor blade and stored dry in paper bags prior before cultivation.
In total, 31 BSCs were collected from 13 pine and 18 beech stands, of which from 23 were managed and 8 were natural forest plots (Table 1).

Culturing, identification and richness of algae
Solid 3N-Bolds Basal Medium (1.5% agar) with vitamins (Starr and Zeikus, 1993) was used for enrichment cultures in Petri dishes (9.5 cm diameter).Several 7-10 mm 2 BSC pieces were cleaned with forceps to remove all roots and leaves to avoid the additional growth of fungi and bacteria, and were placed on the surface of an agar plate under sterile conditions.Plates were incubated at 20°C, 30-35 μmol photons m −2 s −1 (Osram Lumilux Cool White lamps L36W/840) under a light/dark cycle of 16:8 h L:D.The plates were regularly inspected and colonies were identified four to six weeks after incubation using a light microscope (BX51, Olympus) with Nomarski differential interference optics and 1000x magnification.Light micrographs were taken with an Olympus UC30 camera attached to the microscope and processed with the software cellSens Entry (Olympus).For direct observation of BSC samples, pieces of crust were rewetted with tap water, put on slide and analyzed with the above mentioned microscope with a maximumat 400x magnification.
Mucilage of algae was stained with an aqueous solution of methylene blue.Algae Phototrophic microorganisms were identified that belong toas Cyanobacteria, Chlorophyta, Streptophyta and some Stramenopiles (Eustigmatophyceae).Diatoms were regularly observed found in direct observations, but excluded from the analyses as the mentioned enrichment cultivation is not suitable for estimation identification of diatom diversitysthis group of microalgae (e.g.Schulz et al., 2016).
Since enrichment cultivation does not allow a clear conclusion on the abundance of each identified algal taxonspecies,The richness of algae , i.e. the( total number of algae species and cyanobacteria perin each a sample), was used as measurement for diversity rather than diversity indices like evenness, because enrichment cultivation does not allow a clear conclusion about the abundance of each species.As a second parameter for biodiversity, we included showed the similarity between the single plots is shown in terms ofbyas reflected in the presence or/ absence of individual species which combines in order to include not only the total number but alsoand the identity of allthe algal taxa observed.observedspecies.
Additionally, the community composition of the algae as reflected by the presence or absence of individual species was used as a second parameter for diversity estimation.Further.Further, we categorized the identified algae were categorized in filamentous or coccal life form, because both differ in their ecological function.Filamentous algae, in contrast to coccal algae, have the potential to initiate crust-formation and stabilize thesoil particles by gluing them together.

Environmental variables
The natural and managed forest plots were characterized by differences in the silvicultural management intensity.In natural forests, no management was conducted, meaning that fallen trees were left in place and no trees were cut.In managed, ageclass forests, the stands were clear-cut after some years.During the growth phase regular human-induced disturbances occurredregularly disturbed due to, for example, e.g.usage of skid trails and removal of dead trees as well as tree cut.To evaluate the effect of management, the silvicultural management index (SMI) was used.This index takes into account the tree species, stand age and aboveground living and dead wood biomass, i.e. stand density (Schall and Ammer, 2013).The Nnatural forest has a lower SMI than the usedmanaged forest; a pine stand has a higher SMI than a beech stand; high stand density is reflected by a high SMI (Schall and Ammer, 2013).
To assess interactions between BSC biodiversity parametersindicators and environmental parameters, the richness, presence or absence of individual algal community composition of algae andspecies and proportion of filamentous algae was linked to the following environmental parameters: main tree species (pine or beech), silvicultural management intensity (SMI), water content and pH of the bulk soil for all 31 plots (water content and pH kindly provided by I. Schöning, Table 1) and, further, for a subset of the samples (n=19), total C, N and P content, organic and inorganic P proportions, both for labile, moderately labile and stabile P. Latter Data on latter are not shown here but were already presented in detail by Baumann et al. (2017).

Statistical analyses
All statistical analyses were done using the statistical software R version 3.3.0( R Development Core Team, 2009).
Analysis of Variance (ANOVA) was conducted to reveal the effect of environmental parameters on algal and cyanobacteria richness and proportion of filamentous algaespecies; their best predictors were selected by backward elimination stepwise regression analysis based on the BIC (Bayesian information criterion) using 'step' command in R. The correlation between environmental parameters were checked by Pearson correlation (cor and cor.test commands in R).
To reveal correlations of single environmental parameters with the presence or absence of individual algal speciescommunity composition of algae, we applied PerManova (with adonis function in R (Anderson, 2001)) was applied using the Bray-Curtis dissimilarity index (Bray and Curtis, 1957), including permutation test with 1000 permutations.The function "adonis" allows applying non-Euclidean distance metrics and handles both categorical and continuous predictors.For analysis of co-correlation of environmental factors pearsonPearson correlation was used.To test significant differences of environmental factors between tree species, unpaired, two-tailed t-test was performed.
Differences with a p-value below or equal to 0.05 were taken as significant.

Algae identification
In total 521 different algae species and one Cyanobacterium were detected in enrichment cultures of all 31 BSC samples.
Stichococcus bacillaris was the most ubiquitous taxon, observed in 27 out of 31 samples; followed by Coccomyxa simplex and Klebsormidium cf.subtile in 26 out orf 23 samples, respectively.All other algal species were detected in less than 50% of the plots; 22 algal species were observed exclusively at one plot (Figure 2).The total species richness of algae, i.e. the total species number, at each plot ranged from three to 14 species, with the mean of eight and a standard deviation of 2.6 (complete species list is provided in the supplemental Table S1).
The phylum Chlorophyta made up 81% of all detected algale species, followed by Streptophyta (11%) and Stramenopiles (6%).Cyanobacteria were rare in these BSCs, just one species, Microcoleus vaginatus, was observed in only one sample.
In each BSC at least two different filamentous species taxa were detected indicating their importance for BSC formation.
Especially the genus Klebsormidium seemed to be highly important for BSCs in forest: in each BSC at least one of in total three observed morphospecies was found (Supp.Table S1).

Correlation of algae diversity richness with plot characteristics and nutrient content
The silvicultural management intensity was measured by applying the silvicultural management index (SMI), which is based on stand density, tree species and stand age.The gravimetric water content of the bulk soil was correlated with the SMI; the pH was independent of the water content, SMI and the main tree species (Table 2).The N content correlated with the C content and both were independent of the SMI and pH.Total P and the proportion of inorganic P were independent of the C and N content, as well as from pH and SMI (Table 2).
The richness of algal species and the proportion of filamentous algae in BSCs only correlated with SMI, water content and proportion of inorganic phosphorus P (Table 3).All other tested parameters (C and N content, total P, proportion of organic P, pH, main tree species, and soil horizon) were excluded by stepwise model simplification based on the BIC and thus had no measurable effect on the algal species richness or proportion of filamentous algae.A higher SMI resulted in a higher species richness (Figure 2), especially the proportion of coccal algae was enhanced.
The presence or absence of individual algal species in BSCs community composition of the algae significatlysignificantly correlated with the main tree species (15% explained variance) and with the water content (10% explained variance).The SMI and proportion of inorganic P explained each 5% of the variance, but this was not significant (Table 3).

Species composition and abundance
In total 512 microalgal species and one cyanobacterium were identified in all sampled BSCs (Figure 2), which is a similar or slightly lower richness compared to other reports on BSCs from temperate regions at open sites (Langhans et al., 2009;Schulz et al., 2016), but similar or higher compared to previous reports on algae from forest bulk soil (Khaybullina et al., 2010;Novakovskaya and Patova, 2008;Starks et al., 1981).Nevertheless, the given number is most probably an underestimation of the real algal biodiversity richness because our results are based on enrichment cultivation followed by morphological assignment.Enrichment cultivation typically covers only mainly cultivable algae, which represent only a small part of all algae phototrophic microorganisms in the BSCs (Langhans et al., 2009).A recent paper comparing metagenomic data with morphological data based on enrichment cultivation estimated a match of about 10% of all microalgemicroalgae in a polar BSC (Rippin et al., 2018).Furthermore, it is not always possible to distinguish dormant from currently active microalgae.
NeverthelessHowever, direct observation of a BSC sample under the microscope gave gives at least a first hint for the dominant active organisms.Using this approach we could prove that all filamentous algae were abundant and always alive vital in the BSC samples.The morphological identification of algae has known challenges, for example,: e.g.sibling species have similar characteristics but are genetically distant (Potter et al., 1997).To overcome these limitations, researchers proposed to combine molecular and morphological methods, but alsosince molecular techniques alone sometimes also fail to detect some algae taxa based on problems with DNA extraction, appropriate primers etc. (Büdel et al., 2009;Garcia-Pichel et al., 2001).
All observed algal species are known as terrestrial taxa, most of them were also reported in other BSCs (Büdel et al., 2016 and references therein;Ettl and Gärtner, 1995).
Chlorophyceae were the most abundant phylum, which is typical for temperate regions (Büdel et al., 2016).Especially most of the unicellular algae belong to Chlorophyta; a high richness of this soil algae (genera Chlamydomonas, Chloromonas, Chlorococcum, Tetracystis) is characteristic for humid habitats and typical for forest soils Especially most of the unicellular algaetaxa belong to the Chlorophyta, and hence; a high richness of this soil algae (genera such as Chlamydomonas, Chloromonas, Chlorococcum, and Tetracystis) is characteristic for humid habitats and typical for forest soils (Hoffmann 1989).. Cyanobacteria were represented by only one single species.Cyanobacteria are often reported as predominant species in BSCs in arid regions such as Israel and drylands of the USA (Garcia-Pichel et al., 2001;Kidron et al., 2010).Nevertheless, Cyanobacteria are less abundant in temperate regions (Gypser et al., 2016;Langhans et al., 2009;Pluis, 1994) and even rare in acidic soils, as in the forest plots of our study site Schorfheide-Chorin (Hoffmann et al., 2007;Lukešová, 2001;Lukešová and Hoffmann, 1996).Absence or presence in small amount in forest soil is concerning with low pH of soil extract which unfavorable for cyanobacteria (Hollerbakh & Shtina, 1969;Hoffmann, 1989).It seems that Cyanobacteria play only a minor role in forest ecosystems with consequences for the ecological traits that some Cyanobacteria speciestaxa occupy.For example, the ability for nitrogen fixation in phototrophic organisms was only reported from Cyanobacteria and never observed in eukaryotic algae.In forest ecosystems litter and other decomposable biomass provides probably sufficient mineral nitrogen compounds, which might lead to the absence of nitrogen-fixing organisms in these systems in contrast to nitrogen-poor habitats such as dunes or deserts (Langhans et al., 2009;Schulz et al., 2016).
The filamentous alga Klebsormidium was found in nearly all BSCs of our study, whereas species with similar strong filaments (Microcoleus and Xanthonema) were only found occasionally.Filamentous algae can be regarded as key players in BSCs such communities because of their potential as BSC-initiating organisms by building tight networks among soil particles (Büdel et al., 2016).In sSome investigated forest BSCs were formed as well byalso moss protonema can exert a similar function, which hasdue to their filamentous nature and were hence wasere determined as crust-forming organisms (Weber et al. 2016).
However, Klebsormidium seems to be the most important crust-initiating alga in forest ecosystems of Schorfheide-Chorin.
This genus can tolerate a wide range of environmental factors and, thus, has a cosmopolitan distribution in numerous terrestrial and freshwater habitats (Karsten et al., 2016;Rindi et al., 2011 and references therein).Its presence in other terrestrial habitats such as natural rocks in plain and mountainous areas (Mikhailyuk et al., 2008), caves (Vinogradova and Mikhailyuk, 2009), sand dunes (Schulz et al., 2016), tree barks (Freystein et al., 2008), acidic post-mining sites (Lukešová, 2001), bases of urban walls (Rindi and Guiry, 2004) and building facades (Barberousse et al., 2006) is well documented.As many other terrestrial algae, Klebsormidium is tolerant to light exposure during dehydration (Gray et al., 2007).This is a typical situation which BSC algae have to cope with because increase of light in the morning is often associated with dehydration (Raanan et al., 2016).A recent study in Central Europe, however, observed that Klebsormidium is sensitive to increasing light during cellular water loss (Pierangelini et al., 2017).The distribution of Klebsormidium in nearly all samples from Schorfheide-Chorin forest plots may be explained by a lower radiation and also lower evaporation of water in the forest ecosystem compared to open habitats (such as inland dunes), where besides Klebsormidium other filamentous algae were dominant (Langhans et al., 2009;Pluis, 1994).Also, the forest soil pH is rather acidic (min: 3.23; max: 3.86, Table 1) which supports a dominance of Klebsormidium (Škaloud et al., 2014).Thus, the low light availability, low water evaporation and the acidic soil reaction conditions plausibly explain the presence and dominance of Klebsormidium as a potential BSC-initiating algal taxon in nearly all BSCs from Schorfheide-Chorin forest plots.
We identified Tthree morpho-species of the genus Klebsormidium were identified in theour samples investigated (Figure 22).
All three morpho-species were reported from other aeroterrestrial habitats in Central Europe (Glaser et al., 2017;Mikhailyuk et al., 2015).Klebsormidium has exhibits morphological features which can be easily recognized, but the identification down to species level is difficult due to high morphological plasticity (Lokhorst, 1996).And still, in times of molecular identification, the debate on species definition in the genus Klebsormidium is ongoing (Mikhailyuk et al., 2015;Rindi et al., 2017).Therefore, the definition of clades within Klebsormidium was and still is a helpful tool to differentiate between morpho-or genotypes on a species-like level (Rindi et al., 2011).Studies comparing clades at different localities on the one hand observed a global ubiquity, and local endemism on the other hand (Ryšánek et al., 2014).Especially the clade composition seems to differ depending on the habitat.In detail, Klebsormidium cf.flaccidum (B/C clade) was abundant in closed as well as in open habitats, whereas K. cf.nitens and K. cf.subtile (E clade) were predominantly distributed in forest BSCs (Glaser et al., 2017;Mikhailyuk et al., 2015).In this study, however, we also observed in BSCs from forests contained more often Klebsormidium cf.subtile and K. cf.nitens than K. cf.flaccidum.Nevertheless, in desiccation experiments the recovery rates of these clades were similar (Donner et al., 2017a(Donner et al., , 2017b))

Correlation with SMI
The richness of algal species as well as the proportion of coccal algae werewas positively correlated with the silvicultural management index (SMI), which means that we discovered more algal species were discovered in biological soil crustsBSCs from managed than from natural forest ecosystems.tThatis finding correspondsed with conclusions about high algal biodiversity richness on disturbed or cultivated soils (Hollerbakh & Shtina, 1969;Hoffmann, 1989).The SMI reflects the main tree species and the stand density as a result of management practice.Most studies in the Biodiversity Exploratories on soil microorganisms in forests observed rather an effect of the main tree species on the community than of the SMI (Goldmann et al., 2015;Kaiser et al., 2016;Purahong et al., 2014); just only one study on litter decaying fungi and bacteria observed indicated a significant difference between natural and managed beech forests (Purahong et al., 2015).Kaiser et al. (2016) discussed that the different tree species influence the community of soil bacteria by shifting the pH in soil, and hence ; the pH was described in this the mentioned study as the main predictor for bacterial community composition.However, the differences in the bulk soil pH between beech and pine forest were not significant in Schorfheide-Chorin (Table 1) and thus the algae in BSCs were not affected by soil pHthis abiotic parameter.We therefore rejected an effect of the SMI via the pH on the BSC algal species richness in Schorfheide-Chorin.
However, SMI combines other potential factors which may might affect BSC microalgae, namely water regime and light availability due to stand density and tree species.The sampled forest plots in the exploratory Schorfheide-Chorin were dominated by either beech or pine trees, both differing in their light regime: in beech forests the canopy shade changes during spring and therefore radiation on the ground can beis usually higher in winter and spring than in pine forests.Also, the stand density, another parameter of the SMI, could affect the light regime on the ground: higher density would result in less photosynthetic active radiation for photosynthetic active soil microorganisms.The radiation is often coupled with evaporation of pore watersoil moisture (Raanan et al., 2016) and, hence, the stand density could have an indirect effect on the BSC organisms via an altered water regime.Thus, we expect that the SMI was expected to affected the algae algal diversity richness in BSCs via lower light availability and lower evaporation rates.This assumption is well supported by the two-way analysis of water content and SMI, both of which areis described as highly important for algal species richness.Nevertheless, it should be noted that the water content was measured in the bulk soil which might differ from that of BSCs.For future studies on algal biodiversitymicroalgae in BSCs it would be important to examine also available the incident light on the ground and the BSC water content in the BSC.
Although the SMI positively affected the algal richness, the presence or absence of individual algal the community composition wasspeciestaxa was correlated with the main tree species but not with the SMI.Broadleaf litter has a higher quality in terms of a more favorable C:N and C:P ratio compared to coniferous litter (Cleveland and Liptzin, 2007;McGroddy et al., 2004).It might be that the community in pine forest is shifted towards algal species, which can cope better with low nutrient availabilitythe a suboptimal C:N:P ratio.But as mentioned above also other, above mentioned factors (light regime and water evaporation)availability differ between both forest types and could thus have contributed tocause the observed differences in the the occurrence of algal community compositionspeciesintentification.

Correlation with C,/ N, and /P
BSCs have different important ecological functions, such as, for example, BSCs the enhancement of the nutrient content in the top soil layer (Baumann et al., 2017;Evans and Johansen, 1999).To assess the relationship between biodiversity BSC community and biogeochemical cycling in BSCs, the content of total C, N and P and additionally the different P fractions (organic, inorganic, labile and stable fractions) were correlated with algal diversityrichness.Baumann et al. (2017) reported that the presence of BSCs leads to the enhanced content of total C, N and P and in particular the proportion of organic P. The present study shows that therebyWe did not observeAlthough a correlation between the richness of algae was independent ofand the total C, N and P content was not observed, although the presence of BSCs clearly leads to thean enhanced content of total C, N and P and in particular thea higher proportion of organic P (Baumann et al., 2017).HenceThus, we it is assumed that algal species are functional redundant and a low species richness in BSCs can still conduct the functional role of enhancing C, N and P content in BSCs.A more detailed analysis of the P fractions gave a slightly different picture: the proportion of inorganic P was correlated with the proportion of filamentous algae and showeds a tendency to a correlationcorrelate with the richness of BSC algae.Soluble inorganic phosphate originates either from P-mineral weathering, desorption of mineral-bound phosphates or from mineralization of organic matter (Mackey and Paytan, 2009) and can be assimilated by organisms.Thus, a low amount of inorganic P could indicate a high take-up rate of BSC organisms and, thus, a more closed P cycle due to higher algale richness (Baumann et al., 2017).

Conclusion
We observed that biological soil crustsBSCs are able to coexist in temperate forest ecosystems, because natural and humaninduced disturbances, likesuch as wind fall and skid trails, leaveregularly provide free space for crusts to develop.This studies reports fFor the first time we report on the algale biodiversity richness in BSCs from temperate forests are describedwith under different management intensity.The rather acidic forest soil supports a clear dominance of streptophycean Klebsormidiummorphotypes as the main crust-initiating filamentous algae, while Cyanobacteria always play a negligible role. in at temperate forestsour study site.Moss protonema is registered as crust-forming agent in forest ecosystems as well.Higher forest management intensity resulted in a higher richness of algae, especially the proportion of coccal taxa increased.We It is expect reasonable to assume that the land-usesilvicultural management intensity in forests affect the algale biodiversity richness via due to, for example, higher stand density in managed forests, which changes in the light and water regime.(less light in high stand density and in pine forests), and thus,also the which is positively coupled with water evaporation.Increasingregime.
Increasing algal richness in BSCs was supposed to enhance biogeochemical cycling of nutrients, as documented for P compared to bare soils, but this hypothesis could not be proven.
We expected a correlation between the total content of carbon, nitrogen and phosphorusphosphorus, N, and P with the number of algal species or their identity, respectively, because it was As described before, that BSCs enhance the content of C, N and Pnutrients compared to bulk soil (Baumann et al., 2017).In contrast , we observed no correlation between the total content of C, N and P and the species richness of algae and Cyanobacteria.Nevertheless, the fraction of inorganic phosphorusP showed tendencies towards a correlation with the BSC algae in biological soil crustsBSCs, especially with the content of filamentous species.Our Consequently, the present study gives the first hint of a potential relation between the biogeochemical cycles in BSCs and algal species.In our opinion, it is worth to study tThis relation should beshould be studied in more detail, for example, by e.g.gene expression analyses to understand if and how algae in BSCs influence the cycling of phosphorusP.Also, In this study, we observed a relation between the proportion of inorganic P with the biodiversity of algae, especially a positive correlation with the proportion of filamentous algae.Thus, the BSC does not only enhance the total amount of P but its algal biodiversity affects the proportion of the inorganic P. Fforthcoming studies should include other crust-associated organisms, like fungi and bacteria, to identify key players on the ecological role of BSCs in the P cycle.
Competing interests.The authors declare that they have no conflict of interest.Special issue statement.This article is part of the special issue "Biological soil crusts and their role in biogeochemical processes and cycling" Table 1.General inforamation on study sites: Ssample location, main tree species, if the stand is managed or natural forestmanagement status, silvicultural management index (SMI), soil horizon material, on which BSC was growing, water content and pH from bulk soil analyses, and proportion of inorganic phosphorus P as % of from total P (water content and pH were kindly provided by Ingo Schöning); n.d.= not determined., * taken from Baumann et The abbreviations "cf." are in italics in many places in the text, please check.Thanks for the comment, it was corrected.Methods: Study site: How many of the pinus and fagus samples originated from protected vs. managed forests?This information is included now in the text as well as in table 1. page 2, line 3: e.g., Belnap: : : !e.g.Belnap (no comma) p. 2, l. 31: mucilage SHEDS -mucilage SHEATHS maybe?p. 3, l.20: What does DFG stand for?p. 3, l.27: : : :the upper two millimeters of the crust WERE: : : p. 4, l. 18: Community composition based only on algae recovered by cultivation on agar plates does not reflect the real situation.We corrected the wording to presence or absence of indivdiual species.ls.29-31: To overcome these limitations, researchers proposed to combine (!) molecular and morphological methods, SINCE molecular techniques ALONE sometimes ALSO fail to detect some algae.p. 7, ls.7-8: Absence or presence: : : The whole sentence in unclear, please check.p. 7, l. 17: which HAS filamentous nature and WERE determined: : : unify p. 8, l.1: Figure 2 does not show anything about Klebsormidium morphospecies.p. 10, l. 8: bulk soil (Baumann et al., 2017) -space missing

Figure 4 .
Figure 4. Plot of algae richness in BSCs from forests over the silvicultural management index (SMI), natural forest has a low SMI, managed forests a high SMI; the line indicates the best linear fit (slope: 13.6, p<0.001(Anova)) . It is still an open question, which environmental factors caused the slight habitat preferences of the different clades.Additional ecophysiological experiments along with transcriptomic approaches combining potential environmental factors, such as light regimes, desiccation frequency and duration as well asand soil parameters such as pH, might in future explain theseis conspicuous habitat preferences of Klebsormidium clades.

Figure 1 .
Figure 1.Top row: overview of the sampling sites; bottom row: close-up of the sampled crusts.Left pictures were taken from an intensively managed pine forest; right pictures from a natural beech forest.

Figure 2 .
Figure 2. Frequency of occurrence of each algale species in biological soil crusts from forest sites (n=31).

Table 2 :
Pearson CORRELATION...All very specific comments were followed as suggested.

Table 1 : this can be provided in the supplement.
We decided to keep table 1 in the main text but added two information: managed or unmanaged site; proportion of inorganic P 5 keyKey words: biological soil crusts, forest, management intensity, phosphorus, algae richness, Klebsormidium

Table 2 .
al. (2017) Significant Pearson correltation coefficients to reveal correlations between environmental factors, which might affect or be affected by the biodiversity of algae.This co-correlation analysis should support the correct interpretation of potential important factors of the biodiversity.SMI-silvicultural management index; n.s.not significant

Table 3 .
Effect of environmental factors on algae richness, filamentous algae proportion (both estimated by ANOVA) and